Spectroscopy of HD 45166

The Hydrogen and Helium lines are systematically broader than the CNO lines. Assuming that HD 45166 is a double-line spectroscopic binary, it present s an orbital period of P=1.596+/-0.003-day, with an eccentricity of e=0.18+/-0.08. In addition, a search for periodicity using standard techniques reveals that the emission lines present at least two other periods, of 5 and 5 hour.

The secondary star has a spectral type of B7 V and, therefore, should have a mass of about M=4.8M_{sun}_. Given the radial velocity amplitudes, we determined the mass of the hot (primary) star as M=4.2+/-0.7M_{sun}_ and the inclination angle of the system, i=0.77+/-0.09deg. As the eccentricity of the orbit is non zero, the Roche lobes increase and decrease as a function of the orbital phase.

At periastron, the secondary star fills its Roche lobe. The distance to the star has been re-determined as d=1.3+/-0.2kpc and a color excess of E(B-V)=0.155+/-0.007 has been derived. This implies an absolute B magnitude of -0.6 for the primary star and -0.7 for the B7 star.

We suggest that the discrete absorption components (DACs) observed in the ultraviolet with a periodicity similar to the orbital period may be induced by periastron events.